如何将IntPtr转换为流？

public static MemoryStream IntPtrToStream(IntPtr ptr, int size)
{
    MemoryStream stream = new MemoryStream(size);
    BinaryWriter writer = new BinaryWriter(stream);
    writer.Write(ptr.ToPointer(), size);
    stream.Position = 0;
    return stream;
}

public static MemoryStream ByteArrayToStream(byte[] buffer)
{
    MemoryStream stream = new MemoryStream(buffer.Length);
    BinaryWriter writer = new BinaryWriter(stream);
    writer.Write(buffer);
    stream.Position = 0;
    return stream;
}